The flight control of a rotorcraft differs in difficulty and complexity, at least to some extent, as a function of the size and character of the rotorcraft and the attendant operating conditions. Generally speaking, a larger more powerful aircraft may be more forgiving of a variety of changes in operating conditions than would a smaller less powerful aircraft. Still further, removal of the human pilot from within the rotorcraft, as by employing remote and/or autonomous control, may further complicate controllability.
A condition observed during remote control of a small unmanned aerial vehicle (UAV) of the rotorcraft type having a low power-to-weight ratio and coaxial rotors, involves the difficulty in maintaining stable manual longitudinal (pitch) control, particularly in response to rapid shifts in pitch attitude resulting from wind gusts and the like. For example, when the rotorcraft pitches nose up as the result of an input such as a wind gust, the operator will attempt to compensate with an appropriate nose down pitch control response. However, depending upon the rate and magnitude of the corrective action required, the pitch servo control may be driven to saturation, thus limiting the requisite response. In an extreme instance, failure to provide the requisite pitch control for the rotorcraft may result in loss of its control. In an effort to avoid that consequence, the operator may attempt to manually reduce the collective control when the pitch control saturates. However, that action as well requires careful monitoring of the pitch control and rapid adjustment of the collective control, which may severely test the dexterity of the operator flying the UAV rotorcraft. Indeed, it may not be possible to manually respond with sufficient speed and accuracy to avoid loss of control of the rotorcraft.